It is known to use a sail to propel a sailing vessel, ice boat, land sailing vehicle and the like. However, the efficiency of even the most advanced sail designs remains relatively low. In part, this is due to the fact that as the wind fills the sail, it tends to cause the hull to move from the vertical and to lean to one side or to "heel". Sail efficiency declines as the vessel heels because the wind spills out of the sail before it can significantly contribute to forward propulsion and further because ballast is added to maintain the vessel upright to counteract the tendency of the hull to heel which decreases vessel speed.
In an attempt to increase sail efficiency airfoils were adapted for use on sail equipped vessels. Airfoils offer the advantage over conventional sails in that they approach a more perfect foil design. However, they still do not address the problems associated with the effects of heeling. Known airfoils may be rigid or flexible in construction and may be of reversible chamber. Exemplary of the art of wing type sails are U.S. Pat. Nos. 4,563,970; 4,341,176; 4,530,301; 4,624,203 and 4,649,848, the disclosures of which are hereby incorporated by reference.
In view of the foregoing it is an object of the present invention to provide an airfoil adapted to be used to propel a vessel and which reduces the tendency of the vessel to tilt or to heel.
Another object of the present invention is to provide an airfoil adapted to be used to propel a vessel which increases safety by reducing the tendency of the vessel to overturn.
A further object of the present invention is to provide an airfoil adapted to be used to propel a vessel that reduces the vessel ballast requirements.
A still further object of the present invention is to provide an airfoil adapted to be used to propel a vessel that increases the ability of the vessel to reach its planing hull speed.
A still further object of the present invention is to provide an auxiliary wind propulsion system that can be adapted for use on existing motor vessels with a minimum of hull and ballast modification.
A still further object of the present invention is to provide a mechanism for the aerodynamic braking of a vessel.